Conventional techniques for molding internally threaded caps, involving extraction of the molded articles by an unscrewing motion, cannot be used with such closures because the spurs would oppose that motion and shear off during ejection from the mold.
Stripping such a molded closure off a core in its axial direction is equally unavailing since the spurs are held in axially confined undercut recesses of that core.
Possible prior-art solutions solutions include the use of collapsible cores (see, for example, U.S. Pat. No. 3,865,529), yet molds comprising such cores have a rather complex structure and also make it virtually impossible to expedite the setting of the molded article by the cooling of the inner cavity wall of a mold.
These drawbacks are overcome only in part by the provision of a divided core with interfitting sections that can be angularly displaced relative each other to form channels parallel to the axis of the mold for the withdrawal of internal projections of the molded article, e.g. as described in U.S. Pat. No. 3,584,111. Molds of this description, however, are suitable only for articles whose internal projections are sturdy enough to withstand an axial extraction from their recesses without excessive deformation.